SORFC system with non-noble metal electrode compositions

ABSTRACT

A solid oxide regenerative fuel cell includes a ceramic electrolyte, a first electrode which is adapted to be positively biased when the fuel cell operates in a fuel cell mode and in an electrolysis mode, and a second electrode which is adapted to be negatively biased when the fuel cell operates in the fuel cell mode and in the electrolysis mode. The second electrode comprises less than 1 mg/cm 2  of noble metal.

This application is a continuation of U.S. application Ser. No.11/594,797, filed on Nov. 9, 2006, which issued as U.S. Pat. No.7,887,971, which is a divisional application of U.S. application Ser.No. 10/658,275, filed on Sep. 10, 2003, which issued as U.S. Pat. No.7,150,927 B2.

BACKGROUND OF THE INVENTION

The present invention is generally directed to fuel cells and morespecifically to reversible fuel cells and their operation.

Fuel cells are electrochemical devices which can convert energy storedin fuels to electrical energy with high efficiencies. There are classesof fuel cells that also allow reversed operation, such that oxidizedfuel can be reduced back to unoxidized fuel using electrical energy asan input.

One type of reversible or regenerative fuel cell is the solid oxideregenerative fuel cell (SORFC) which generates electrical energy andreactant product from fuel and oxidizer in a fuel cell or discharge modeand which generates the fuel and oxidant from the reactant product andthe electrical energy in an electrolysis or charge mode. The SORFCcontains a ceramic electrolyte, a positive or oxygen electrode and anegative or fuel electrode. The electrolyte may be yttria stabilizedzirconia (“YSZ”) or doped ceria. The positive electrode is exposed to anoxidizer, such as air, in the fuel cell mode and to a generated oxidant,such as oxygen gas, in the electrolysis mode. The positive electrode maybe made of a ceramic material, such as lanthanum strontium manganite(“LSM”) having a formula (La,Sr)MnO₃ or lanthanum strontium cobaltite(LSCo) having a formula (La,Sr)CoO₃. The negative electrode is exposedto a fuel, such as hydrogen gas, in a fuel cell mode and to water vapor(i.e., reactant product) in the electrolysis mode. Since the negativeelectrode is exposed to water vapor, it is made entirely of a noblemetal or contains a large amount of noble metal which does not oxidizewhen exposed to water vapor. For example, the negative electrode may bemade of platinum.

However, the noble metals are expensive and increase the cost of thefuel cell. In contrast, the prior art acknowledges that the negativeelectrodes cannot be made from a non-noble metal in a SORFC because suchelectrodes are oxidized by the water vapor in the electrolysis mode. Forexample, an article by K. Eguchi et al. in Solid State Ionics 86-88(1996) 1245-1249 states on page 1246 that a cell with Ni-YSZ electrodesis not suitable for a solid oxide electrolyzer cell. The article furtherstates on page 1247 that that a high concentration of steam (i.e., watervapor) caused the deterioration of a Ni-YSZ electrode and that a nobleor precious metal negative electrode is preferred.

BRIEF SUMMARY OF THE INVENTION

One preferred aspect of the present invention provides a solid oxideregenerative fuel cell, comprising a ceramic electrolyte, a firstelectrode which is adapted to be positively biased when the fuel celloperates in a fuel cell mode and in an electrolysis mode, and a secondelectrode which is adapted to be negatively biased when the fuel celloperates in the fuel cell mode and in the electrolysis mode. The secondelectrode comprises less than 1 mg/cm² of noble metal.

Another preferred aspect of the present invention provides a method ofoperating a solid oxide regenerative fuel cell, comprising operating thesolid oxide regenerative fuel cell in a fuel cell mode by providing afuel to a negative electrode and providing an oxidizer to a positiveelectrode to generate electricity and water vapor at the negativeelectrode. The method further comprises operating the solid oxideregenerative fuel cell in an electrolysis mode by providing electricityto the fuel cell and providing water vapor to the negative electrode togenerate fuel at the negative electrode and oxygen at the positiveelectrode. The method further comprises providing a sufficient reducingatmosphere to the negative electrode when the solid oxide regenerativefuel cell operates in the electrolysis mode to prevent the negativeelectrode from oxidizing. The negative electrode comprises less than 1mg/cm² of noble metal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a SORFC system operating in anelectrolysis mode according to a preferred embodiment of the presentinvention.

FIG. 2 is a schematic illustration of a SORFC system operating in a fuelcell mode according to a preferred embodiment of the present invention.

FIG. 3 is a schematic cross section of a single SORFC operating in theelectrolysis mode according to a preferred embodiment of the presentinvention.

FIG. 4 is a schematic cross section of a single SORFC operating in thefuel cell mode according to a preferred embodiment of the presentinvention.

FIG. 5 is a plot of current potential and power density versus currentdensity of a SORFC cell according to a specific example of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present inventors have realized that SORFC negative (i.e., fuel)electrode may contain no noble metals or a small amount of noble metals,such as less than 1 mg/cm² of noble metal, if a sufficient reducingatmosphere is provided to the negative electrode when the fuel celloperates in the electrolysis mode to prevent the negative electrode fromoxidizing. The use of cheaper and/or more common conductive materials inthe negative electrode reduces the cost of the SORFC and improvesoperational performance.

As used herein, the term noble metal includes gold, iridium, palladium,platinum, rhodium, osmium and silver. These metals are also known asprecious metals. Preferably, the negative electrode contains less than20 weight percent of noble metal. More preferably, the negativeelectrode contains less than 0.1 mg/cm² of noble metal and less than 1weight percent of noble metal. Most preferably, the negative electrodecontains no noble metal or an unavoidable trace impurity amount of noblemetal. Furthermore, it is preferred that the positive electrode alsocontains no noble metal or an unavoidable trace impurity amount of noblemetal.

As used herein, the term SORFC (i.e., solid oxide regenerative fuelcell) includes a ceramic electrolyte, a positive or oxygen electrodewhich is adapted to be positively biased when the fuel cell operates ina fuel cell mode and in an electrolysis mode, and a negative or fuelelectrode which is adapted to be negatively biased when the fuel celloperates in the fuel cell mode and in the electrolysis mode. Oxygen ionsare conducted through the ceramic electrolyte from the positiveelectrode to the negative electrode when the fuel cell operates in thefuel cell mode and from the negative electrode to the positive electrodewhen the fuel cell operates in the electrolysis mode.

Any suitable materials may be used for the electrolyte and theelectrodes. For example, the negative electrode may comprise a non-noblemetal, such as at least one of Ni, Cu, Fe or a combination thereof withan ionic conducting phase (i.e., a cermet). In one preferred aspect ofthe invention, the negative electrode consists essentially of a Ni-YSZcermet (i.e., a nickel-yttria stabilized zirconia cermet). Any suitableweight ratio of nickel to YSZ may be used in the electrode, such as aratio of 30:70 to 95:5, preferably 65:35. The electrolyte may compriseany suitable ceramic, such as YSZ and/or doped ceria.

In another preferred aspect of the invention, the negative electrodeconsists essentially of a Ni-doped ceria cermet. Any suitable weightratio of nickel to doped ceria may be used in the electrode, such as aratio of 30:70 to 95:5, preferably 65:35. In this case, the electrolytepreferably comprises a doped ceria electrolyte or a combinationelectrolyte having a doped ceria portion or layer in contact with thenegative electrode and a YSZ portion in contact with the positiveelectrode. The ceria may be doped with any suitable dopant, such as a Scdopant or a rare earth dopant selected from Gd and Sm, in an amountsufficient to render the ceria to be ionically conducting.

The positive electrode may comprise any suitable material. Preferably,the positive electrode comprises a conductive perovskite ceramicmaterial selected from LSM, LSCo, LCo, LSF, LSCoF, PSM or a combinationthereof with an ionic conducting phase. Lanthanum strontium manganite(“LSM”) preferably has a formula (La_(x),Sr_(1-x))MnO₃ where x rangesfrom 0.6 to 0.99, preferably from 0.8 to 0.85. Lanthanum strontiumcobaltite (“LSCo”) preferably has a formula (La_(x),Sr_(1-x))CoO₃ wherex ranges from 0.6 to 0.99, preferably 0.8 to 0.85. If x is equal to one,then the electrode material comprises LCo. Lanthanum strontium ferrite(“LSF”) preferably has a formula (La_(x)Sr_(1-x))FeO₃ where x rangesfrom 0.4 to 0.99, preferably from 0.6 to 0.7. Lanthanum strontium cobaltferrite (“LSCoF”) preferably has a formula(La_(x),Sr_(1-x))(Fe_(y),Co_(1-y))O₃ where x ranges from 0.4 to 0.99,preferably from 0.6 to 0.7 and y ranges from 0.01 to 0.99, preferablyfrom 0.7 to 0.8. Praseodymium Strontium Manganite (“PSM”) preferably hasa formula (Pr_(x),Sr_(1-x))MnO₃ where x ranges from 0.6 to 0.99,preferably from 0.8 to 0.85. The perovskite electrode materials mayoptionally be admixed with the electrode ceramics, such as YSZ and dopedceria, such as GDC (gadolinium doped ceria). Other suitable pervoskiteelectrode materials may also be used.

As used herein, “a sufficient reducing atmosphere to prevent thenegative electrode from oxidizing” comprises any suitable reducing gaswhich when mixed with water vapor provided to the negative electrodeduring electrolysis mode prevents the negative electrode from oxidizingto an extent which prevents it from operating according to its designedparameters during its expected life span, such as for at least onemonth, preferably at least one year, such as one to ten years, forexample. Preferably, hydrogen is used as the reducing gas. However,other gases, such as forming gas (a nitrogen/hydrogen mixture) andcarbon monoxide may also be used alone or in combination with hydrogen.The maximum ratio of water vapor to reducing gas provided to thenegative electrode during the electrolysis mode depends on the materialof the negative electrode and on the type of reducing gas used. Somenegative electrode materials require more reducing gas to preventoxidation that other negative electrode materials. For example, if ahydrogen reducing gas is used for a Ni-YSZ electrode, then the water tohydrogen ratio is preferably 8 or less, for example 0.1 to 8, such as0.4 to 5 or 0.44 to 1. However, the water to hydrogen ratio may bedifferent than the ratio provided above depending on various factors,such as the electrode composition, the overall gas composition providedto the negative electrode and other factors, while still preventing thenegative electrode from oxidizing to an extent which prevents it fromoperating according to its designed parameters during its expected lifespan. Preferably, the reducing atmosphere (i.e., the reducing gas) doesnot chemically participate in the electrolysis process and is cycledthrough the fuel cell without being consumed.

FIG. 1 illustrates a SORFC system 1 operating in the electrolysis orcharge mode. The system 1 contains a schematically illustrated SORFC 10.While only a single SORFC 10 is shown, it should be understood that thesystem 1 preferably contains a stack of SORFCs, containing a pluralityof electrolytes, positive electrodes and negative electrodes. The system1 also contains a fuel storage vessel 101, such as a hydrogen tank, anoptional fuel compressor 103, a water-hydrogen separator/water storagedevice 105, a water pump 107, an oxidizer blower 109, a fuel bleed valve111 and optional water, oxidizer and compressor valves 113, 115 and 117,respectively. The system 1 also contains heat exchangers 119 and 121which preheat the inlet streams into the fuel cell 10 using the fuelcell exhaust streams. The system further contains fuel and oxidizerconduits, such as pipes, hoses or other suitable gas and liquidconduits, which connect the above mentioned components together.

The system contains a reducing gas conduit 123 which provides asufficient reducing atmosphere to the negative electrode of the fuelcell 10 when the fuel cell operates in the electrolysis mode to preventthe negative electrode from oxidizing. Preferably, the reducing gas 123conduit also comprises a fuel conduit which is used to provide fuel tothe negative electrode during the fuel cell or discharge mode. Thus, thereducing gas in the electrolysis mode preferably, but not necessarily,comprises the same gas as the fuel which is used in the fuel cell mode.In the electrolysis mode, the bleed valve 111 located in the reducinggas conduit is partially opened to provide a smaller amount offuel/reducing gas to the fuel cell than in the fuel cell mode.

Preferably, the reducing gas/fuel comprises hydrogen and the reducinggas conduit 123 comprises a hydrogen conduit operatively connected to atleast one of a hydrogen compressor 103 and the hydrogen fuel storagevessel 101. The term operatively connected means that the conduit 123may be directly or indirectly connected to the compressor 103 and/orvessel 101 to allow hydrogen to flow from the compressor 103 and/orvessel 101 through the conduit 123 into the fuel cell. The conduit 123is operatively connected to the fuel inlet of a fuel cell 10 (i.e., tothe inlet of the fuel cell stack).

The water-hydrogen separator 105 is also operatively connected to thefuel inlet of the fuel cell via the water inlet conduit 125. Theseparator 105 provides water to the negative electrode of the fuel cell10 when the fuel cell 10 operates in the electrolysis mode. Preferably,the conduits 123 and 125 converge at the three way valve 113, and inletconduit 127 provides the water and reducing gas from valve 113 to thenegative electrode of the fuel cell 10.

A fuel outlet of the fuel cell 10 is operatively connected to awater-hydrogen separator 105 via a fuel exhaust conduit 129. Conduit 129removes water from the negative electrode when the fuel cell operates inthe fuel cell mode. An oxygen exhaust conduit 131 removes oxygengenerated at the positive electrode when the fuel cell operates in theelectrolysis mode. An oxidizer inlet conduit 133 provides an oxidizer,such as air or oxygen, to the positive electrode of the fuel cell 10when the fuel cell operates in the fuel cell mode. In the electrolysismode, the conduit 133 is closed by valve 115.

FIG. 2 illustrates the SORFC system 1 operating in the fuel cell ordischarge mode. The system 1 is the same, except that the bleed valve111 is opened to a greater amount than in the electrolysis mode, theoxidizer valve 115 is open instead of closed and the water valve 113either totally or partially closes the water conduit 125.

A method of operating the solid oxide regenerative fuel cell system 1will now be described. In the fuel cell mode shown in FIG. 2, a fuel,such as hydrogen, carbon monoxide and/or a hydrocarbon gas, such asmethane, is provided to the negative electrode of the fuel cell 10 fromstorage vessel 101 through conduits 123 and 127. The fuel is preheatedin the heat exchanger 119. If desired, some water from theseparator/storage device 105 is provided via conduits 125 and 127 to thenegative electrode of the fuel cell as well. Alternatively, the watermay be provided from a water pipe rather than from storage.

An oxidizer, such as oxygen or air is provided to the positive electrodeof the fuel cell 10 through conduit 133. This generates electricity(i.e., electrical energy) and water vapor at the negative electrode. Theunused oxidizer is discharged through conduit 131. The water vaporreactant product along with unused fuel, such as hydrogen, and othergases, such as carbon monoxide, are discharged from the fuel cellthrough conduit 129 into the separator 105. The hydrogen is separatedfrom water in the separator and is provided into the compressor 103through conduit 135. The compressor 103 cycles the hydrogen back intothe fuel cell 10.

In the electrolysis mode shown in FIG. 1, electricity is provided to thefuel cell. Water vapor is provided to the negative electrode of the fuelcell 10 from the separator/storage device 105 or from a water pipethrough conduits 125 and 127. A sufficient reducing atmosphere, such ashydrogen gas, is also provided to the negative electrode throughconduits 123 and 127. For example, at start-up of the SORFC operation,when the compressor 103 does not usually run, the hydrogen may beprovided from the storage vessel 101. Subsequently, when the compressor103 becomes operational at steady state, it provides hydrogen to theconduit 123 and to the storage vessel 101.

This generates fuel, such as hydrogen, at the negative electrode, andoxygen at the positive electrode of the fuel cell. The hydrogen,including the hydrogen generated in the electrolysis of water vaporreaction and the hydrogen provided from conduit 123 along with remainingunreacted water vapor are provided from the fuel cell 10 through conduit129 to the separator 105. The water-hydrogen separator 105 separates thehydrogen from water, with the water being either stored or discharged.The separated hydrogen is provided to the compressor 103 through conduit135. The compressor provides a first portion of the compressed hydrogento the hydrogen storage vessel 101 and provides a second portion of thecompressed hydrogen to the negative electrode of the fuel cell 10through conduit 125 to maintain the sufficient reducing atmosphere atthe negative electrode. The oxygen generated during the electrolysisreaction is discharged through conduit 131.

Preferably, the fuel cell 10 is cycled between the fuel cell mode andthe electrolysis mode at least 30 times, such as 30 to 3,000 times.During the cycles, when the fuel cell operates in the electrolysis mode,the bleed valve 111 bleeds a first sufficient amount of hydrogen from atleast one of the hydrogen compressor and the hydrogen fuel storagevessel through the hydrogen conduit 123 to the negative electrode of thefuel cell to prevent the negative electrode from oxidizing. Providing areducing atmosphere on the negative electrode during the electrolysismode allows the use of non-noble materials in the electrode which alsomaintains compatibility for the electrolysis operation.

When the fuel cell operates in the fuel cell mode, the bleed valveprovides hydrogen fuel from the hydrogen storage vessel through thehydrogen conduit 123 to the negative electrode in a second amountgreater than the first amount. In other words, the first amount ofreducing gas should be a small amount of reducing gas, but sufficient toprevent oxidation of the negative electrode.

It should be noted that the hydrogen conduit 123 provides a sufficientamount of reducing gas to the plurality of negative electrodes of a fuelcell stack to prevent all negative electrodes of the stack fromoxidizing. Therefore the negative electrodes of the SORFC stack aremaintained in a reducing atmosphere, preventing oxidation of theelectrode materials at elevated temperatures in the range 600-1000° C.

In alternative embodiments of the present invention, separate storagevessels are used to store fuel and the reducing gas. Preferably, thisoccurs when the fuel and reducing gas comprise different gases. Forexample, the fuel may comprise a hydrocarbon fuel rather than hydrogen,or forming gas or carbon monoxide is used as a reducing gas. In thiscase, a separate reducing gas storage vessel, such as a hydrogen, carbonmonoxide or forming gas storage tank or pipe may be used to provide thereducing gas into the fuel cell 10 in the electrolysis mode, while thefuel storage vessel 101 is used to provide fuel into the fuel cell inthe fuel cell mode.

A single SORFC 10 operating in the electrolysis mode is shown in FIG. 3.The SORFC contains an anode (positive) electrode 11, an electrolyte 13and a cathode (negative) electrode 12. An anode gas chamber 14 is formedbetween the electrolyte 13 and an anode side interconnect (not shown forsimplicity). A cathode gas chamber 15 is formed between the electrolyte13 and a cathode side interconnect (also not shown for simplicity).

A reaction product gas mixture 17 may contain primarily water withreducing gas, such as hydrogen. Alternatively, the reaction product gasmixture 17 may contain primarily water vapor and carbon dioxide if acarbon containing gas or liquid, such as methane, is used as a fuel.Hydrogen, carbon monoxide or forming gas is also added to the gasmixture as the reducing gas.

The reaction product gas mixture 17 is introduced into the cathode gaschamber 15. A direct current power source (not shown) is connected tothe anode electrode 11 and the cathode electrode 12 in such a way thatwhen electrical current is flowing, the anode electrode 11 takes on apositive voltage charge and the cathode electrode 12 takes on a negativevoltage charge. When the electric current is flowing, the gas mixture 17gives up oxygen ions 16 to form cathode discharge mixture 19 consistingprimarily of hydrogen and optionally carbon monoxide if mixture 17contained carbon dioxide. Oxygen ions 16 transport across theelectrolyte 13 under the electrical current. The oxygen ions 16 areconverted into the oxidant, such as oxygen gas 18 on the anode electrode11 under the influence of the electrical current. The oxygen gas 18 isdischarged from the anode chamber 14, while the electrolysis product(e.g., hydrogen and optionally carbon monoxide) is collected from thecathode chamber. If carbon monoxide is present in the product, then theproduct may be converted to methane fuel and water in a Sabatierreactor.

A single SORFC 20 operating in the fuel cell mode is shown in FIG. 4.SORFC 20 is the same as SORFC 10, except that the cathode and anodedesignations of its electrodes are reversed. Cathode (positive)electrode 21 is the same electrode as that identified as the anode(positive) electrode 11 in FIG. 3 when operating in the electrolysismode. Anode (negative) electrode 22 is the same electrode as thatidentified as the cathode (negative) electrode 12 in FIG. 3 whenoperating in the electrolysis mode. Solid oxide electrolyte 23 is thesame electrolyte as that identified as electrolyte 13 in FIG. 4 whenoperating in the electrolysis mode. Cathode gas chamber 24 is the samegas chamber as that identified as the anode gas chamber 14 in FIG. 3when operating in the electrolysis mode. Anode gas chamber 25 is thesame gas chamber as that identified as the cathode gas chamber 15 inFIG. 3 when operating in the electrolysis mode.

A fuel gas 27 is introduced into the anode gas chamber 25. An oxidizer,such as air or oxygen gas 28 is introduced into the cathode chamber 24.The fuel may comprise hydrogen, a hydrocarbon gas, such as methane,and/or carbon monoxide. Water may be added to the fuel if desired. Anelectrical fuel cell load (not shown) is applied to the SORFC 20 and theoxygen gas 28 forms oxygen ions 26 under the influence of the electricalload. Oxygen ions 26 transport across the electrolyte 23 under theinfluence of the electrical current. On the anode electrode 22, theoxygen ions 26 combine with hydrogen and optionally carbon, if present,from gas mixture 27 to form gas mixture 29 containing water vapor andoptionally carbon dioxide, if a carbon containing gas is present in thefuel 27. Gas mixture 29 is discharged from the anode chamber and storedas the reaction product. In the process described above, the SORFC 20has made electrical energy or power, which is output through itselectrodes.

The SORFC systems described herein may have other embodiments andconfigurations, as desired. Other components, such as fuel side exhauststream condensers, heat exchangers, heat-driven heat pumps, turbines,additional gas separation devices, hydrogen separators which separatehydrogen from the fuel exhaust and provide hydrogen for external use,fuel preprocessing subsystems, fuel reformers, water-gas shift reactors,and Sabatier reactors which form methane from hydrogen and carbonmonoxide, may be added if desired, as described, for example, in U.S.application Ser. No. 10/300,021, filed on Nov. 20, 2002, in U.S.Provisional Application Ser. No. 60/461,190, filed on Apr. 9, 2003, andin U.S. application Ser. No. 10/446,704, filed on May 29, 2003 allincorporated herein by reference in their entirety.

The following specific example is provided for illustration only andshould not be considered limiting on the scope of the present invention.FIG. 5 illustrates the plot of cell potential and power density versuscurrent density for a single 10 cm² SORFC cell using a test bed thatmodels the inlet gas streams as described with respect to FIGS. 1 and 2above. The SORFC cell contains the following components. The negative orfuel electrode is a Ni-YSZ cermet electrode containing 65 weight percentNi and 35 weight percent YSZ. This electrode is 27 microns thick and ismade by screen printing on the electrolyte and being fired to 1350° C.The electrolyte is a YSZ electrolyte that is 300 microns thick. Theelectrolyte is tape cast and fired to 1550° C. The positive or oxygenelectrode is an LSM electrode that is 39 microns thick. This electrodeis made by screen printing on the electrolyte and firing to 1200° C.

The negative electrode is fed with a constant 300 sccm of H₂ passingthrough a humidifier at a set temperature. The charge (i.e.,electrolysis) mode is run with the humidifier set to 70° C. or 30.75%H₂O. This provides an H₂O to H₂ ratio of 0.44 to the negative electrode.One discharge (i.e., fuel cell) mode is run with the humidifier set to70° C. or 30.75% H₂O, while another discharge (i.e., fuel cell) mode isrun with the humidifier set to 29° C. or 3.95% H₂O. The H₂O to H₂ ratiois 0.44 and 0.04, respectively, for the respective discharge mode runs.Table 1 below lists the negative electrode conditions for the variousmodes of operation with ambient pressure reactants.

H₂ H₂O FLOW HUMIDIFIER PERCENT H₂O/H₂ OPERATING MODE [sccm] TEMP [° C.][%] RATIO Charge Mode 300 70 30.75 0.44 Discharge Mode 1 300 70 30.750.44 (“wet hydrogen fuel”) Discharge Mode 2 300 29 3.95 0.04 (“dryhydrogen fuel”)

As shown in FIG. 5, this fuel cell with a negative electrode whichcontains no noble metal is successfully operated in both charge anddischarge modes and exhibits acceptable current-voltage andcurrent-power characteristics for reversible operation.

The foregoing description of the invention has been presented forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed, andmodifications and variations are possible in light of the aboveteachings or may be acquired from practice of the invention. Thedescription was chosen in order to explain the principles of theinvention and its practical application. It is intended that the scopeof the invention be defined by the claims appended hereto, and theirequivalents.

1. A solid oxide regenerative fuel cell, comprising: a ceramicelectrolyte; a first electrode which is adapted to be positively biasedwhen the fuel cell operates in a fuel cell mode and in an electrolysismode; a second electrode which is adapted to be negatively biased whenthe fuel cell operates in the fuel cell mode and in the electrolysismode; and a first device which provides a sufficient reducing atmosphereto the second electrode when the fuel cell operates in the electrolysismode to prevent the second electrode from oxidizing; wherein the secondelectrode comprises less than 1 mg/cm² of noble metal.
 2. The fuel cellof claim 1, wherein the first device comprises a hydrogen conduitoperatively connected to at least one of a hydrogen compressor and ahydrogen fuel storage vessel.
 3. The fuel cell of claim 2, wherein thehydrogen conduit is operatively connected to a fuel inlet of a fuel cellstack and a fuel outlet of the fuel cell stack is operatively connectedto a water-hydrogen separator.
 4. The fuel cell of claim 3, wherein thewater-hydrogen separator is operatively connected to the fuel inlet ofthe fuel cell stack and is adapted to provide water to the secondelectrode when the fuel cell operates in the electrolysis mode.
 5. Thefuel cell of claim 2, further comprising a valve which is adapted tobleed a first sufficient amount of hydrogen from at least one of thehydrogen compressor and the hydrogen fuel storage vessel through thehydrogen conduit to the second electrode to prevent the second electrodefrom oxidizing when the fuel cell operates in the electrolysis mode andwhich is adapted to provide hydrogen fuel from the hydrogen storagevessel through the hydrogen conduit to the second electrode in a secondamount greater than the first amount when the fuel cell operates in thefuel cell mode.
 6. The fuel cell of claim 1, wherein the first devicecomprises a forming gas conduit operatively connected to a forming gasstorage vessel.
 7. The fuel cell of claim 1, wherein the first devicecomprises a carbon monoxide conduit operatively connected to a carbonmonoxide storage vessel.
 8. The fuel cell of claim 3, further comprisinga water pump located between the water-hydrogen separator and thehydrogen conduit, the water pump configured to pump water from thewater-hydrogen separator to the hydrogen conduit.
 9. The fuel cell ofclaim 3, further comprising a heat exchanger configured to preheathydrogen from the hydrogen conduit prior to delivering the hydrogen tothe second electrode.